Tuesday, November 20, 2018

Why your mental map of the world is (probably) wrong

Contrary to the map many of us have in our minds,
almost all of South America is farther east than North America.
Courtesy David Rumsey Map Collection

From National Geographic by Betty Matson

These are some of the most common geographic misconceptions that are both surprising and surprisingly hard to correct.

Most of us have a rough map of the world in our minds that we use any time we think about places.
But these mental maps aren’t necessarily reliable.
In fact, many of the maps in our heads share the same errors, some of which are quite large—and surprisingly resistant to correction.

For instance, we all know that South America is south of North America, of course.
But you may be surprised by the fact that virtually the entire South American continent is east of Florida.
There are lots of possible reasons for geographical misconceptions like this one, says cartographer John Nelson.
Mental maps are necessarily simplifications, and Nelson suspects the misplaced Americas may be partly a result of their names.
After all, it’s not called Southeast America.

Nelson’s father, who was a geography professor at Central Michigan University, wrote a paper about geographical misconceptions in 1992 with some of his colleagues and input from Nelson’s mother, a high-school geography teacher.
“I actually remember them talking about this research paper over dinners when I was younger,” Nelson says.
He recently revisited the paper and put together a story map that highlights three common misplacements mentioned in the paper, including the true longitudinal relationship between the Americas.

Misplaced Continents

Most of Africa is north of the equator, though on many mental maps it is mostly in the southern hemisphere directly across the Atlantic from South America.
Courtesy John Nelson, ESRI

Another commonly misplaced continent is Africa.
North Americans tend to think of Africa as a located almost entirely in the southern hemisphere, similar to South America.
But in reality, around two-thirds of Africa is north of the equator.
“Africa actually extends northward to about the same latitude as Norfolk, Virginia,” the paper’s authors write.

Europe is also often placed much farther south on mental maps than it really is, appearing directly across the Atlantic from the contiguous United States.
But it actually lines up better with Canada: Paris is further north than Montreal, Barcelona is at a similar latitude as Chicago, and Venice lines up with Portland, Oregon.

Nelson suspects that climate might play a role in this misconception.
Western Europe is relatively warm for its latitude thanks to the Gulf Stream, which brings warmer water from the Gulf of Mexico across the Atlantic and gives Europe its so-called Mediterranean climate.
The warmer temperatures are more similar to the climate of the lower 48 states than Canada’s.

Many people think of Europe as sitting directly across the Atlantic Ocean from the United States, when it is actually farther to the north.
Venice, Italy is at the same latitude as Minneapolis, Minn.
as shown by the dotted line on this map.
Courtesy John Nelson, ESRI

People also tend to keep their mental maps simple by aligning them with the four cardinal directions, according to the paper’s authors.
So it’s easier for North Americans to think of Europe as due west and South America as due south.

Size Matters

Locations aren’t the only way our mental maps can be wrong; we also have misconceptions about the relative size of things.
This may be due in part to the nature of two-dimensional maps.
Flattening a three-dimensional globe onto a flat surface isn’t possible without some distortion.
This is especially obvious for maps that use certain projections—ways of representing the Earth’s curved surface on a flat map—such as the popular Mercator projection, which could be found on many 20th-century classroom walls.

This 1912 map uses the Mercator projection, which inflates the size of land near the poles such that Greenland appears to be the same size as South America when in fact it is only one-eighth as big.
Courtesy David Rumsey Map Collection

Mercator maps distort the shape and relative size of continents, particularly near the poles.
This is why Greenland appears to be similar in size to all of South America on Mercator maps, when in fact South America is more than eight times larger than Greenland.

While you may have already been aware of Greenland’s extreme exaggeration on some maps, other inconsistencies are more surprising.
For example, Brazil isn’t that impressive on many maps, but in reality it’s bigger than the entire contiguous United States and almost as large as Canada.
And Alaska, which is a giant on Mercator maps, is actually a little smaller than Libya.

The popular Mercator projection distorts the relative size of landmasses, exaggerating the size of land near the poles as compared to areas near the equator.
This map shows that in reality, Brazil is almost as large as Canada, even though it appears to be much smaller on Mercator maps.
Screenshot courtesy of THETRUESIZE.COM;
Map data ©Google, Inegi, Orion-Me

Thinking about the world in two-dimensions also distorts our ideas about how to get from one place to another, says geographer Anthony Robinson of Penn State University.
If you draw a line on a flat map from Washington D.C.
to Shanghai, China, the most direct route appears to be due west over the United States and the Pacific Ocean.
But Robinson says he’s been on plenty of flights to Asia where people are surprised to hear the pilot say they’ll be flying over the North Pole.
When looking at a globe instead of a flat map, it makes sense.
“That's far and away the shortest way to get there,” Robinson says.

The Persistence of Memory

None of these geographic misconceptions would be surprising for a student to have on the first day of geography class, but even once we’ve learned the truth, the errors on our mental maps tend to persist.
One reason for this may be that our conceptions of the world are basically summaries of the geography, says cartographer Dylan Moriarty, who is an interactive designer at the Wall Street Journal.
The mental map is a simplification, similar to the the subway map of New York City, he says.
“The approximation is just more useful and practical.”

Our mental maps are usually simplifications of the actual geography and locations of things relative to each other, much like the New York City subway map is.
Courtesy New York City Subway Mao ©Metropolitan Transportation Authority

Our physical experience of the world may come into play as well, Robinson says.
“I think it must have something to do with both the limits of our observable perception of space and time, and the fact that we are disrupting that constantly with technology and methods of transportation and things that compress those things and make them nonfactors.”

Whatever the reason, these mental map errors are so pervasive and stubborn that even professionals have them.
A 1985 study of mental world maps found that geographers had the same misconceptions of the relative latitude of cities in North America and Europe as everyone else.
Cartographers aren’t immune either.
The “eastiness” of South America still surprises Nelson sometimes.
“I really have to look again at a map and be like, is that really the case?” he says.
“And sure enough it is.”

Links :

Monday, November 19, 2018

How will ship routing look in fifteen years?

 From Maritime Executive by Michael O'Neil, StormGeo

This past September, StormGeo announced its acquisition of Nautisk — a leading supplier of maritime charts and publications.
By allowing us to integrate our routing and weather services with state-of-the-art charts and publications, this move pushes our company full-speed into the future of shipping technology.
It has also made me think about how ship routing will look in years to come, and how it will likely be delivered in a very different way than it is today.

Ships will be much more digitally connected with increasing access to high-speed internet.
This will allow route suggestions to be delivered in a format that the Master can accept directly into the ECDIS (Electronic Chart Display and Information System), rather than having to load them manually.
This is why we’re moving towards integrating all routing services more tightly with voyage planning and route transfer directly to ECDIS.

 BVS (Bon Voyage System) route optimization

At present, a Master using BVS (Bon Voyage System) can send a route from the ship to our operations center.
We then evaluate it and pass a route back to the Master’s BVS.
In the future, much more complicated route plans could be passed back and forth addressing any number of weather or environmental concerns.
The improved quality of communications, sea-keeping data and weather data will allow for lower operating expenses as ships run more efficiently.

Given that the future of shipping will include a number of ships operated from shore as well as fully autonomous ships, I foresee routing information often being delivered to a shore-side operations facility rather than the vessel itself.
For those that continue to have a crew on board, information could be projected onto the bridge windows in a type of 3-D overlay, which would enhance situational awareness.

While vessel motion sensor technology is continuously improving, it is likely that ship routing systems will be able to take this data and provide more precise recommendations to the Master (on board or on shore) regarding vessel motions.
Having more precise vessel motion data helps to ensure the utmost in crew, ship and cargo safety.

  MOL starts initiative to develop enhanced operational support tool, aiming at a new level of safety
Captain’s Dynamic Operation System for Counter planning and Analysis (Capt.’s DOSCA),
provided by Weathernews Inc.

Ship Routing’s Impact on Fuel Efficiency

In addition to the sensors mentioned above, there will also be engine sensors that report on all engineering systems and the cargo on board.
These sensors and the data they send can allow for optimized heating/cooling of cargo, engage or disengage the shaft generator, and make changes in the heading and speed of the ship.
The latter will reduce sloshing for liquid gas carriers and reduce the risk of parametric rolling for container ships.

 credit : StormGeo

Beyond sensors, there will be tools on board the ship and in the shore-side operations centers to better manage constant power, which, when properly implemented, has a profound impact on fuel efficiency.
This, of course, is a service we provide today but it is subject to certain human factors on board the ship that limit the efficacy.

ChartCo and MeteoGroup Announce Long-Term Partnership

Where Will Autonomous Ships Be Utilized?

There are significant safety and economic reasons to move towards semi-autonomous shipping, which for me, refers to ships that will have a crew operating the navigation and engineering functions from a shore-side operations center.
From a safety perspective, I foresee shore-side operators working with extremely sophisticated tools that will continuously check decisions and thus reduce human error.

Some are predicting the advent of remotely operated vessels by as early as 2020.
While it may be an industry norm to have fully autonomous ships in 2030, I expect they will still be very much the minority.
I believe these ships will mainly operate in lower traffic areas and on short voyages of four to five days or less.
It’s important to note, however, that in 2016, shorter voyages made up close to 60 percent of the total maritime transport of goods to and from the main EU ports.
So these ships may actually be in great demand.

The Age of Customization

Despite all this, there is one area where not much will change: the need for recommended routes.
It will take much larger leaps in technology to develop a ship capable of sailing through any weather.
A vessel capable of withstanding the heaviest weather Mother Nature can produce would not be effective in carrying cargo or passengers.

With the innovation within sensors, new ship designs and improved shore to vessel communication, solutions for the industry are becoming more ship-specific.
From vessel-specific hull curves to the capture and use of vessel-specific sensor data, solutions will be more customized than ever before.
Companies using these tools will be able to precisely recommend the main engine load and RPM’s to achieve a superior level of fuel efficiency.

Whatever the future, StormGeo will always keep an eye on what lies ahead, while continuing to employ lessons learned from decades of supporting ships along safe and economic routes.

Links :

Sunday, November 18, 2018

Submarine ARA San Juan located

The Ministry of Defense and the Armada Argentina inform that on this date, having investigated the point of interest N°24 reported by Ocean Infinity, through the observation made with an ROV at 800 meters deep, has given positive identification to ARA SanJuan

Localization of POI24 with the GeoGarage platform (SHN nautical chart)

From NatSouth

How the ARA San Juan was ultimately found?

Argentine Navy Captain Enrique Balbi presents images from the wreck of the submarine ARA SanJuan.
Pressure hull imploded with bow section, sail and propeller torn off.
see Clarin photos / Armada Argentina

It is with a sense of a little relief but also deep sadness to learn today that the ARA San Juan submarine missing for a year was finally located.

geographical coverage of Area1 search zone
source : @Ocean__Infinity

On 23 Nov, the Argentine Navy released the tragic news of the loss of the submarine, where it confirmed a "singular, abnormal, short, violent & non-nuclear event" consistent with an explosion, took place on 15th November.

 Map with the clues detected by the Argentina Navy given to Ocean Infinity
Ocean Infinity signed a $7.5 million contract with the government to search for the vessel for at least 60 days.
However, the company would only receive the money if the San Juan ARA was found.

The ‘Seabed Constructor’ contracted by the Argentine government located the submarine after an extensive and exhaustive detailed search of two areas off the Patagonian coast.

Area 1 for search

 The "Seabed Constructor" is repositioning toward Site 1, area 15A-4,
to investigate with ROV point of interest POI #24.
source : @Armada_Arg

Hydroacoustic stations HA10 (Ascension Island) and HA04 (Crozet) detected a signal from an underwater impulsive event that occurred at 13:51 GMT on 15 November 2017.
source :  International Monitoring System (IMS) Division, part of the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO)

The location of the event is as follows: Event Latitude: -46.12 deg; Event Longitude: -59.69 deg which is in the vicinity of the last known location of the ARA San Juan.
Today we can know that there is a difference of between 15 and 18 kilometers between the place where the explosion was detected and the place where ARA San Juan was found.

PART 1 — The first series of searches

Last year, numerous ships with various search capabilities crisscrossed a huge swath of the seabed, as determined by the last reported position of the submarine and also acoustics findings reported by the CTBTO

 See image for the intensity of the search by 30th December 2017
source MarineTraffic (@MikeChillit)

As I remarked last year, these are just the AIS tracks of ships involved.
There were other ships who weren’t on AIS, such as some of the other participating search support Argentine Navy ships (ARA La Argentina, ARA Robinson, ARA Sarandí, ARA Puerto Argentino).

A couple of months later the ‘Yantar’ Russian vessel also covered again a lot of the search area.
But the submarine fell 300 to 400 meters after imploding and landed on the upper wall of a canyon.
So even Yantar didn’t see it.
Very hard to detect. 
source : @juanmab

Initial 2017-2018 search
Here a roll of honour for the ships involved in the prolonged initial search phase from November 2017 to end of December 2017.
Several of these ships also continued their search into the first quarter of 2018.
(In alphabetical order):
  • RV Dr. Victor Angelescu – Argentine fisheries oceanographic research vessel
  • RV Atlantis- US - WHOI research oceanographic ship
  • ARA Austral (Argentine Navy) 
  • RV Cabo de Hornos (Chilean Navy)
  • ARA Islas Malvinas (Argentine Navy)
  • ARA Puerto Argentino (Argentine Navy)
  • ARA Puerto Deseado (Argentine Navy)
  • MV Skandi Patagonia (Offshore Support Vessel contracted by US Navy)
  • RFS ‘Yantar’ - Russia - Naval oceanographic ship
Back-up support (Argentina Navy)
  • ARA Sarandi
  • ARA La Argentina
  • ARA Robinson
? (there are more –  rest assured I will add when I get the names)

Other ships
  • NSS "Felinto Perry" (Brazilian Navy)
  • “Sophie Siem” (Offshore Support Vessel contracted by US Navy)
  • HMS Clyde (Royal Navy — UK)
The series of initial searches were ultimately inconclusive.
Subsequently, the Argentinian authorities took the decision to resume the search for the submarine in late October following the signing of a "no cure no fee basis" contract with the company Ocean Infinity.

PART 2: Searching the seabed - techniques

How was the search done?

I outlined the principles of seafloor survey and searching in a blog post last year, but I will summarize it here.  The steps in locating a sunken ship:
  1. bathymetric profiling with multibeam echo-sounder of the seabed
  2. by detailed profiling multi-beam sonar array  (combined  with side scan either with an AUV or on a ‘sledge’ towed astern of mothership).
  3. The images obtained are digitally processed & analysed for subsequent verification;
  4. Verification is done by sending down an ROV for visual inspection of the object.
Multi-beam sonar-  (MBES) a ship equipped with this type of sonar will travel along certain tracks, (called mowing the lawn), to survey a band of the seabed.
The ship sends out multiple ‘sonar’ pings that go down to the seabed at all different angles  (fan-shaped pattern).
Each individual ping is returned back up as backscatter and they are received back onboard.
The returned echoes are thus recorded as a function of time.
The approximate result is shown in the image.

As the ship gradually moves forward, an image (a sort of 'scan') of the morphology of the sea floor is obtained and objects that stand out  (in this case side-scan imagery of  2 sunken Chinese fishing boats).
Essentially it is a continuous band of individual backscattered returns (swath) of depth soundings.
However, due to the distance between a ship and the sea floor, the resolution of the sonar ‘beams’ returned are hampered (limited) for various reasons and there is also 'noise' that affects the sonar data.
So, to get a finer resolution, especially in areas of complex sea floor morphology, (as it is the case of the ARA San Juan location), surveys 'scans' closer to the sea-floor are needed.
The seabed profile of the search area is complex: from a fairly flat continental shelf (top of image) that drops down, with numerous ravines, (gullies / canyons).

Profile of sea-floor in search area.
Source: Armada Argentina (Nov. 2017)

Hence, the use of autonomous underwater vehicle (AUV or UUV) that are able to ‘fly’ closer to the seabed.
For even more finer resolution scan and collecting images, a remotely operated vehicle (ROV) can be used.

The AUV also sends out the same kind of sonar pings, but the data obtained is of much higher resolution.
This data is received on the mothership and it is also sent over to shore-side experts for post-processing.
Thus, specific aspects of the sea floor can then be looked at in greater detail.
This process is required to obtain the desired mapping product, (in this case to identify a "Points of Interest" for subsequent ROV close-up inspections).
The AUVs used in the search for the ARA San Juan had both side-scan and multi-beam bathymetric sonar.

This is was what the ‘Seabed Constructor’ doing for several months.
Side scan and multi-beam backscatter sonar comparison:
Side-scan Sonar literally scans a wide swath of the sea-floor as shown in the picture (with a towed sledge unit).

Side-Scan Sonar is an (almost) continuous signal, whereas MBES is not so quite continuous because it is consists of one backscatter value per beam.

@Armada_Arg's images of PoI D006_001 in ARA SanJuan search show something very reflective & the AUV has imaged it with side scan sonar (SSS) from both sides.
The two SSS views are shown side-by-side.

 The SMF bathymetry image shows the approximate position & depth for ARA San Juan.
The navy said Saturday that the ARA San Juan was located at a depth of 907 meters (2,975 feet).
Authorities said the vessel was sitting in a canyon, and that its depth and location were among the reasons it had not been found during an earlier search of the area. 
The submarine’s location at the bottom of the rugged ocean floor is in the same area where a multinational operation that included the U.S. and 16 other nations had scoured last year after the vessel disappeared. 
All of the ships passed through this zone, including the Argentine navy, and never detected anything. 

This combination of technology is not only used to search for wrecks, but it is also used in the marine biology, offshore industry and geophysical fields.

 Source: Marine Technology News (accessed 2017)

It is of interest to note that only about 15% of the world’s seas and oceans have been surveyed with multi-beam sonar systems.

 Links :

Saturday, November 17, 2018

Canada CHS layer update in the GeoGarage platform

72 nautical charts have been updated & 1 new chart added

NOAA : How can we assist you?

NOAA Office of Coast Survey’s new ASSIST interface.


NOAA makes it easier to submit a comment or report a nautical chart error

On November 16, 2018, NOAA released ASSIST, a new system for submitting questions and reporting nautical chart errors to NOAA’s Office of Coast Survey.
ASSIST has a mobile-friendly design and improved user interface that allows customers to access the system conveniently from any device.
This new tool replaces Coast Survey’s Inquiry and Discrepancy Management System (IDMS), a database that collected nearly 20,000 comments, inquiries, and discrepancy reports since 2008. ASSIST is available from: https://www.nauticalcharts.noaa.gov/customer-service/assist/

ASSIST offers new features including the ability to:
  • Tag your submission on a NOAA chart, map, or satellite imagery
  • Enter reports from a cell phone or other mobile device
  • Comment or report an error using a single form
These improvements streamline the internal Coast Survey workflow, allowing faster, more efficient responses to customers.

Weightless jellies

Jellies have two kinds of skin tissues: an outer exchange layer and an inner "stomach skin".
The frilly parts in the center are called oral arms—projections of the stomach made of gastrodermis that digest food at a distance

Pacific Sea Nettles blissfully at home in the Georgia Aquarium, Atlanta, Georgia.
I was struck by their beauty. Like little spaceships floating in the depths of space.
Graceful, elegant, constantly moving, drifting.
As I filmed, I listened to the crowd as they came and went.
Everyone with children told their child: "Look! They will sting you!"
Not one person in the crowd in the hour that I was there filming commented on the Sea Nettle's beauty. Not one. What does this say about us?

Oh, comb on now! We have two species of comb jelly sharing their exhibit at the moment—the lobed comb jelly Bolinopsis infundibulum and the sea gooseberry Pleurobrachia bachei. That there's a well-coiffed duo!

Links :

Friday, November 16, 2018

What if Greece extends its Territorial Waters to 12 Miles in the Aegean?

From GreekReporter by Tasos Kokkinidis

Former Foreign Minister Nikos Kotzias made a final announcement in October as he handed the ministry’s portfolio to Alexis Tsipras.
He said Greece is ready to extend its territorial waters from 6 to 12 nautical miles.

In the first stage, he said, Greece will expand its sovereignty towards the west from the Diapontia Islands, a cluster of small islands in the Ionian Sea, to Antikythera, an island lying between the Peloponnese and Crete.
But the plan is to also do the same in the Aegean.

Kotzias said that the move constitutes the “first extension of the country’s sovereignty since the Dodecanese became part of Greece in 1947.”
Extension in the Ionian is unlikely to cause any objections from its neighbors Italy and Albania.

 Greece-Turkey (National Geographic 1958)

But, the Aegean is a different proposition altogether.
Turkey has threatened in the past that such a move, which it says in effect turns the Aegean into a Greek lake, is a cause of war (casus belli).

Map of the Aegean islands, indicating date of incorporation into Greece.

Law of the Sea

Territorial waters are an extension to the sea of the national sovereignty of a country beyond its shores.
They are considered to be part of the country’s national territory.

They give the littoral state full control over air navigation in the airspace above, and partial control over shipping, although foreign ships (both civil and military) are normally guaranteed innocent passage through territorial waters.

Greece has a legal right to extend its territorial sea to 12 nautical miles, as provided for by the United Nations Convention on the Law of the Sea.

Virtually all coastal states abide by the Law of the Sea, including Turkey, which since 1964 has expanded its territorial waters in the Black Sea and the Mediterranean to 12 nautical miles.

When ratifying the Convention, Greece tabled a statement declaring that “the time and place of exercising these rights … is a matter arising from its national strategy.”

Successive Greek governments refrained from exercising this legal right.
Six nautical miles have been in force since 1936, and since then there has been a continuing debate on whether Greece should extend to 12 nautical miles.

A Turkish coast guard ship patrols in the Aegean Sea off the Turkish coast

Turkey’s threat

If Greece extends its territorial waters in the Aegean, it will increase its control from the current 43 percent to 71 percent.
International waters will be reduced from 49 percent to less than 20 percent. (see maps above)

This is why Turkey has threatened war.
It claims that the Aegean is a special case and if the provisions of the Law of the Sea are applied, Turkey will be cut off from the Sea.

Imia, the two small rocky islands that lie in the Aegean Sea and have been a source of dispute between the two nations in 1996.
At the back, the Small Imia and on the front of the picture Big Imia.
Localization of th tiny barren islets of Imia/Kardak, situated between the Dodecanese island chain and the Turkish mainland
Imia islands with the GeoGarage platform (NGA chart)

 ICAO map, 1955
source : HRI
Greece rejects Turkey’s arguments saying that under the Law of the Sea the right of passage is fully safeguarded and even expanded.
By making use of these rights, even warships from other countries can move undisturbed from Greek territorial waters and through narrow passages between the islands, as is done today.

Tensions over the 12-mile question ran highest between the two countries in the early 1990s, when the Law of the Sea was going to come into force.
On 9 June 1995, the Turkish parliament officially declared that unilateral action by Greece would constitute a casus belli.

This declaration has been condemned by Greece as a violation of the Charter of the United Nations, which forbids “the threat or use of force against the territorial integrity or political independence of any state”.

Links :

Thursday, November 15, 2018

Greenland ice sheet hides huge 'impact crater'

 A large impact crater beneath Hiawatha Glacier in northwest Greenland

From BBC by Jonathan Amos

What looks to be a large impact crater has been identified beneath the Greenland ice sheet.

The 31km-wide depression came to light when scientists examined radar images of the island's bedrock.

Localization with the GeoGarage platform (DGA nautical chart)

Space view: The semi-circular margin of the ice sheet traces the outline of the crater
Natural History Museum of Denmark

Investigations suggest the feature was probably dug out by a 1.5km-wide iron asteroid sometime between about 12,000 and three million years ago.

A map of the bedrock of Greenland.
It would be the most northerly crater on Earth

But without drilling through nearly 1km of ice to sample the bed directly, scientists can't be more specific.
"We will endeavour to do this; it would certainly be the best way to get the 'dead fish on the table', so to speak," Prof Kurt Kjær, from the Danish Museum of Natural History, told BBC News.

In a remote area of northwest Greenland, an international team of scientists has made a stunning discovery, buried beneath a kilometer of ice.
It’s a meteor impact crater, 300 meters deep and bigger than Paris or the Beltway around Washington, DC.
It is one of the 25 largest known impact craters on Earth, and the first found under any of our planet’s ice sheets.
The researchers first spotted the crater in July 2015, while they were inspecting a new map of the topography beneath Greenland's ice sheet that used ice-penetrating radar data primarily from Operation IceBridge, an ongoing NASA airborne mission to track changes in polar ice, and earlier NASA airborne missions in Greenland.

If confirmed, the crater would be the first of any size that has been observed under one of Earth's continental ice sheets.
The discovery is reported in the journal Science Advances.

Kurt Kjær collects sand transported from under the glacier

What does the crater look like?

The putative impact crater is located right on the northwest margin of the Greenland Ice Sheet, underneath what is known as Hiawatha Glacier.

Additional high-resolution radar imagery gathered by Prof Kjær's team clearly shows a circular structure that is elevated at its rim and at its centre - both classic traits.
But because the depression is covered by up to 980m of ice, the scientists have so far had to rely on indirect studies.

A map of the bedrock topography beneath the ice sheet

What is the supporting evidence?

Meltwaters running out from under Hiawatha Glacier into the Nares Strait carry sediments from the depression.
In these sediments are quartz grains which have been subjected to enormous shock pressures, of the type that would be experienced in an impact.

Quartz grains show evidence of having experienced shock pressures

Other river sediments have revealed unusual ratios in the concentrations of different metals.
"The profile we saw was an enrichment of rhodium, a depletion of platinum, and an enrichment of palladium," explained team-member Dr Iain McDonald, from Cardiff University, UK.
"We got very excited about this because we realised we weren't looking at a stony meteorite, but an iron meteorite - and not just any old iron meteorite; it had to be quite an unusual composition."

Such metal objects that fall to Earth are thought to be the smashed up innards of bodies that almost became planets at the start of the Solar System.

The signatures identified by Dr McDonald are relatively close to those in iron meteorite fragments collected at Cape York not far from the Hiawatha site. It's not inconceivable, the team argues, that the Cape York material represents pieces that came away from the main asteroid object as it moved towards its collision with Earth.

The Hiawatha Glacier cuts across the rim of the crater

What are the doubts?

One concerns the absence of any trace of the impact in several cores that have been drilled through the ice sheet to the south.
At the very least, these might have been expected to incorporate the dust that fell out of the sky after the event.

The other head-scratcher is the absence in the vicinity of the Hiawatha site of any rocky material that would have been ejected outwards from the crater on impact.

Prof Kjær says these missing signatures might be explained by a very shallow angle of impact that took most of the ejecta to the north.
And if the fall-out area was covered in ice, it's possible any debris was later transported away.
"We know that at one time the Greenland Ice Sheet was joined to the Canadian Ice Sheet, and flowed out into the Nares Strait. If you wanted to find this material today, you'd have to do deep drilling in the ocean," Prof Kjær explained.

A view of the bedrock below the ice facing northwest, toward the sea, shows the terrain of the crater.
In addition the rim surrounding the feature, the researchers behind the discovery also spotted a slight rise in the center.
Such a rise is a fairly common feature in impact craters, but not diagnostic of how the gape formed
Credit: Natural History Museum of Denmark/Cryospheric Sciences Lab/NASA Goddard Space Flight Center/Greenbelt, MD, USA

What are the age constraints?

The team knows the crater must be older than roughly 12,000 years because the undisturbed ice layers above the depression can be lined up with the layers in drill cores that have been directly dated.

And they estimate an age younger than three million years based on an assessment of likely rock erosion rates, both within the crater and on nearby terrains. But the only way to get a definitive age for the crater would be to drill down and collect rocks for laboratory dating.

An artist's depiction of an iron asteroid hurtling through space

How does this connect with other ideas?

If the impact was right at near-end of the age window then it will surely re-ignite interest in the so-called Younger Dryas impact hypothesis.
The Younger Dryas was a period of strong cooling in the middle of the climatic warming that occurred as the Earth emerged from the height of last ice age.

An illustration of an airplane using radar to map the topography below the ice sheet.

Some have argued that an asteroid impact could have been responsible for this cooling blip - and the accompanying extinction of many animal groups that occurred at the same time across North America.
Others, though, have been critical of the hypothesis, not least because no crater could be associated with such an event.
The Hiawatha depression is likely now to fan the dying embers of this old debate.

Dr Mathieu Morlighem, a team-member from the University of California, Irvine, US, commented: "When you think about it, the bed below the ice sheets has to have impact craters that have not been explored yet, and there may even be some in Antarctica as well, but more radar measurements are necessary to locate them, and dating them is extremely challenging."

Links :